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<p>Allows values of integer type to be used in expressions directly.
</p>
<h3><span class="mw-headline" id="Syntax">Syntax</span></h3>
<p>An integer constant is a <a href="value_category.html" title="c/language/value category">non-lvalue</a> expression of the form
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">decimal-constant</span> <span class="t-spar">integer-suffix</span><span class="t-mark">(optional)</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">octal-constant</span> <span class="t-spar">integer-suffix</span><span class="t-mark">(optional)</span>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">hex-constant</span> <span class="t-spar">integer-suffix</span><span class="t-mark">(optional)</span>
</td>
<td> (3)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">binary-constant</span> <span class="t-spar">integer-suffix</span><span class="t-mark">(optional)</span>
</td>
<td> (4)
</td>
<td> <span class="t-mark-rev t-since-c23">(since C23)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>where
</p>
<ul><li> <span class="t-spar">decimal-constant</span> is a non-zero decimal digit (<code>1</code>, <code>2</code>, <code>3</code>, <code>4</code>, <code>5</code>, <code>6</code>, <code>7</code>, <code>8</code>, <code>9</code>), followed by zero or more decimal digits (<code>0</code>, <code>1</code>, <code>2</code>, <code>3</code>, <code>4</code>, <code>5</code>, <code>6</code>, <code>7</code>, <code>8</code>, <code>9</code>)
</li><li> <span class="t-spar">octal-constant</span> is the digit zero (<code>0</code>) followed by zero or more octal digits (<code>0</code>, <code>1</code>, <code>2</code>, <code>3</code>, <code>4</code>, <code>5</code>, <code>6</code>, <code>7</code>)
</li><li> <span class="t-spar">hex-constant</span> is the character sequence <code>0x</code> or the character sequence <code>0X</code> followed by one or more hexadecimal digits (<code>0</code>, <code>1</code>, <code>2</code>, <code>3</code>, <code>4</code>, <code>5</code>, <code>6</code>, <code>7</code>, <code>8</code>, <code>9</code>, <code>a</code>, <code>A</code>, <code>b</code>, <code>B</code>, <code>c</code>, <code>C</code>, <code>d</code>, <code>D</code>, <code>e</code>, <code>E</code>, <code>f</code>, <code>F</code>)
</li><li> <span class="t-spar">binary-constant</span> is the character sequence <code>0b</code> or the character sequence <code>0B</code> followed by one or more binary digits (<code>0</code>, <code>1</code>)
</li><li> <span class="t-spar">integer-suffix</span>, if provided, may contain one or both of the following (if both are provided, they may appear in any order):
</li></ul>
<dl><dd><ul><li> <span class="t-spar">unsigned-suffix</span> (the character <code>u</code> or the character <code>U</code>)
</li><li> <span class="t-spar">long-suffix</span> (the character <code>l</code> or the character <code>L</code>) <span class="t-rev-inl t-since-c99"><span>or the <span class="t-spar">long-long-suffix</span> (the character sequence <code>ll</code> or the character sequence <code>LL</code>)</span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span>
</li></ul>
</dd></dl>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c23"><td>
<p>Optional single quotes (<code>'</code>) may be inserted between the digits as a separator. They are ignored by the compiler.
</p>
</td>
<td><span class="t-mark-rev t-since-c23">(since C23)</span></td></tr>
</table>
<h3><span class="mw-headline" id="Explanation">Explanation</span></h3>
<div class="t-li1"><span class="t-li">1)</span> Decimal integer constant (base 10, the first digit is the most significant).</div>
<div class="t-li1"><span class="t-li">2)</span> Octal integer constant (base 8, the first digit is the most significant).</div>
<div class="t-li1"><span class="t-li">3)</span> Hexadecimal integer constant (base 16, the first digit is the most significant, the letters 'a' through 'f' represent the decimal values 10 through 15).</div>
<div class="t-li1"><span class="t-li">4)</span> Binary integer constant (base 2, the first digit is the most significant)</div>
<p>The following variables are initialized to the same value:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> d <span class="sy1">=</span> <span class="nu0">42</span><span class="sy4">;</span>
<span class="kw4">int</span> o <span class="sy1">=</span> <span class="nu8">052</span><span class="sy4">;</span>
<span class="kw4">int</span> x <span class="sy1">=</span> <span class="nu12">0x2a</span><span class="sy4">;</span>
<span class="kw4">int</span> X <span class="sy1">=</span> <span class="nu12">0X2A</span><span class="sy4">;</span>
<span class="kw4">int</span> b <span class="sy1">=</span> <span class="nu6">0b101010</span><span class="sy4">;</span> <span class="co1">// C23</span></pre></div></div>
<p>The following variables are also initialized to the same value:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l1 <span class="sy1">=</span> 18446744073709550592ull<span class="sy4">;</span> <span class="co1">// C99</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l2 <span class="sy1">=</span> <span class="nu0">18</span><span class="st0">'446'</span><span class="nu0">744</span><span class="st0">'073'</span><span class="nu0">709</span><span class="st0">'550'</span>592llu<span class="sy4">;</span> <span class="co1">// C23</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l3 <span class="sy1">=</span> <span class="nu0">1844</span><span class="st0">'6744'</span><span class="nu8">0737</span><span class="st0">'0955'</span>0592uLL<span class="sy4">;</span> <span class="co1">// C23</span>
<span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> l4 <span class="sy1">=</span> <span class="nu0">184467</span><span class="st0">'440737'</span><span class="nu0">0</span><span class="st0">'95505'</span>92LLU<span class="sy4">;</span> <span class="co1">// C23</span></pre></div></div>
<h3><span class="mw-headline" id="The_type_of_the_integer_constant">The type of the integer constant</span></h3>
<p>The type of the integer constant is the first type in which the value can fit, from the list of types which depends on which numeric base and which <span class="t-spar">integer-suffix</span> was used.
</p>
<table class="wikitable">

<tr style="text-align:center">
<th colspan="3"> Types allowed for integer constants
</th></tr>
<tr style="text-align:center">
<td> suffix
</td>
<td> decimal bases
</td>
<td> other bases
</td></tr>
<tr style="text-align:left">
<td> no suffix
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span> <span class="t-mark-rev t-until-c99">(until C99)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span> <span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td></tr>
<tr>
<td> <code>u</code> or <code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td></tr>
<tr>
<td> <code>l</code> or <code>L</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-until-c99">(until C99)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span><br>
<span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td></tr>
<tr>
<td> both <code>l</code>/<code>L</code> and <code>u</code>/<code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td></tr>
<tr>
<td> <code>ll</code> or <code>LL</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</p>
</td></tr>
<tr>
<td> both <code>ll</code>/<code>LL</code> and <code>u</code>/<code>U</code>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">long</span> <span class="kw4">long</span> <span class="kw4">int</span></span></span><span class="t-mark-rev t-since-c99">(since C99)</span>
</td></tr></table>
<p>If the value of the integer constant is too big to fit in any of the types allowed by suffix/base combination and the compiler supports extended integer types (such as <span class="t-c"><span class="mw-geshi c source-c">__int128</span></span>), the constant may be given the extended integer type; otherwise, the program is ill-formed.
</p>
<h3><span class="mw-headline" id="Notes">Notes</span></h3>
<p>Letters in the integer constants are case-insensitive: <code>0xDeAdBaBeU</code> and <code>0XdeadBABEu</code> represent the same number <span class="t-rev-inl t-since-c99"><span>(one exception is the <span class="t-spar">long-long-suffix</span>, which is either <code>ll</code> or <code>LL</code>, never <code>lL</code> or <code>Ll</code>)</span> <span><span class="t-mark-rev t-since-c99">(since C99)</span></span></span>
</p><p>There are no negative integer constants. Expressions such as <span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">-</span><span class="nu0">1</span></span></span> apply the <a href="operator_arithmetic.html" title="c/language/operator arithmetic">unary minus operator</a> to the value represented by the constant, which may involve implicit <a href="conversion.html" title="c/language/conversion">type conversions</a>.
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-c99"><td>
<p>When used in a controlling expression of <a href="../preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>
#if</tt></a> or <a href="../preprocessor/conditional.html" title="c/preprocessor/conditional"><tt>
#elif</tt></a>, all signed integer constants act as if they have type <span class="t-lc"><a href="../types/integer.html" title="c/types/integer">intmax_t</a></span> and all unsigned integer constants act as if they have type <span class="t-lc"><a href="../types/integer.html" title="c/types/integer">uintmax_t</a></span>.
</p>
</td>
<td><span class="t-mark-rev t-since-c99">(since C99)</span></td></tr>
</table>
<p>Integer constants may be used in <a href="constant_expression.html" title="c/language/constant expression">integer constant expressions</a>.
</p><p>Due to <a href="translation_phases.html#maximal_munch" title="c/language/translation phases">maximal munch</a>, hexadecimal integer constants ending in <code>e</code> and <code>E</code>, when followed by the operators <code>+</code> or <code>-</code>, must be separated from the operator with whitespace or parentheses in the source:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">int</span> x <span class="sy1">=</span> <span class="nu12">0xE</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span>   <span class="co1">// error</span>
<span class="kw4">int</span> y <span class="sy1">=</span> <span class="nu12">0xa</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span>   <span class="co1">// OK</span>
<span class="kw4">int</span> z <span class="sy1">=</span> <span class="nu12">0xE</span> <span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span>  <span class="co1">// OK</span>
<span class="kw4">int</span> q <span class="sy1">=</span> <span class="br0">(</span><span class="nu12">0xE</span><span class="br0">)</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy4">;</span> <span class="co1">// OK</span></pre></div></div>
<p>Otherwise, a single invalid preprocessing number token is formed, which causes further analysis to fail.
</p>
<h3><span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;inttypes.h&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"123 = %d<span class="es1">\n</span>"</span>, <span class="nu0">123</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"0123 = %d<span class="es1">\n</span>"</span>, <span class="nu8">0123</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"0x123 = %d<span class="es1">\n</span>"</span>, <span class="nu12">0x123</span><span class="br0">)</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"12345678901234567890ull = %llu<span class="es1">\n</span>"</span>, 12345678901234567890ull<span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// the type is a 64-bit type (unsigned long long or possibly unsigned long)</span>
    <span class="co1">// even without a long suffix</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"12345678901234567890u = %"</span><a href="../types/integer.html"><span class="kw207">PRIu64</span></a><span class="st0">"<span class="es1">\n</span>"</span>, 12345678901234567890u <span class="br0">)</span><span class="sy4">;</span>
 
<span class="co1">//  printf("%lld\n", -9223372036854775808); // ERROR</span>
<span class="co1">// the value 9223372036854775808 cannot fit in signed long long, which is the</span>
<span class="co1">// biggest type allowed for unsuffixed decimal integer constant</span>
 
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%llu<span class="es1">\n</span>"</span>, <span class="sy2">-</span>9223372036854775808ull <span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// unary minus applied to unsigned value subtracts it from 2^64,</span>
    <span class="co1">// this gives unsigned 9223372036854775808 </span>
 
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%lld<span class="es1">\n</span>"</span>, <span class="sy2">-</span>9223372036854775807ull <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="co1">// correct way to form signed value -9223372036854775808</span>
<span class="br0">}</span></pre></div></div>
<p>Output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">123 = 123
0123 = 83
0x123 = 291
12345678901234567890ull = 12345678901234567890
12345678901234567890u = 12345678901234567890
9223372036854775808
-9223372036854775808</pre></div></div> 
</div>
<h3><span class="mw-headline" id="References">References</span></h3>
<div class="t-ref-std-17">
<ul><li> C17 standard (ISO/IEC 9899:2018): 
</li></ul>
<dl><dd><ul><li> 6.4.4.1 Integer constants (p: 45-46)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd><ul><li> 6.4.4.1 Integer constants (p: 62-64)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd><ul><li> 6.4.4.1 Integer constants (p: 54-56)
</li></ul>
</dd></dl>
</div>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990): 
</li></ul>
<dl><dd><ul><li> 3.1.3.2 Integer constants 
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id="See_also">See also</span></h3>
<table class="t-dsc-begin">

</table>

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